A while back I heard about
http://www.bookcrossing.com/
Interesting idea but I have never tried it yet.
The idea is to release the book somewhere public with a Free book sticker and info about the bookcrossing site. So if your lucky someone will pick it up and register or is already a member so you can follow the book around the world as it get read and release again.
The website also allow you to see which book has been release in your regions.